Factors regulating the expression of virulence factors of Vibrio cholerae (VC) and cholera-like E. coli (EC) will be studied. In vitro assays for the detection of EC enterotoxin and enterotoxigenic strains will be developed. Techniques to differentiate pathogenic EC from normal flora organisms will be assigned. Pathogens from patients and selected laboratory strains made pathogenic by mating and transduction of the EC enterotoxin plasmid will be compared with normal flora and isogenic parental non-pathogens. A phage typing system to distinguish pathogenic EC from non-pathogens will be based on acquisition of unique surface properties and/or plasmid directed restriction mechanisms. Morphological, nutritional, and biochemical differences between pathogenic and nonpathogenic VC and EC will be investigated to attempt to identify virulence factors and/or diagnostic characteristics. The genetic factors regulating EC enterotoxigenicity will be correlated with biochemical parameters in attempts to produce EC enterotoxin in a defined culture medium.